1. Field of the Invention
The present invention relates to a method of aligning at least two images to be scanned and a scanning apparatus for such alignment, where each image has at least one associated alignment area or mark positioned at a given position in relation to the image.
2. Description of Related Art
Alignment of this type is predominantly performed in order to superpose e.g. a number of colour separations, which are typically screened, of an original image or integrating these separations with text in the graphic industry.
In the art, separating the colours of a colour original into e.g. the well-known CMYK or YCMB (Yellow, Cyan, Magenta, Black) colour separations is performed using a computer and suitable software. This separation is performed in order to be able to reproduce the original in e.g. a printing process using the base colours of the colour separation.
In order to be able to precisely position these e.g. four individual and separate representations of the image, the separation also provides alignment or registering marks precisely positioned in relation to the actual image.
Depending on the apparatus producing the colour separations, these alignment or registering marks may be crosses in the film material representing the separations, or the marks may be holes, indentations or notches therein.
In the situation where holes, notches or indentations are provided, these are used in order to precisely position the separations in e.g. the printing machine.
EP 0 200 814 A1 discloses a method for registering colour separation film in order to provide the films with register holes for use in a separate reproduction process.
In the other situation where the marks are crosses or other types of marks or where selected image areas are used for alignment, this positioning in the printing machine may be more difficult.
The same problem may be seen when e.g. desiring to scan the separations to electronically superpose these, as the separations should be positioned very precisely on the scanner.
At present, this positioning of the images is performed by fixing the images on e.g. sheets of transparent film or job-sheets having registering holes for engagement with registering pins on the scanner, in positions where all separations are superposed when positioned on the scanner. Typically, the positioning error should be less than 5/100 mm, whereby this work is quite time consuming.
This positioning or aligning of the separations may be carried out based on the alignment marks, but is also possible to select corresponding image areas of each colour separation and use these selected areas as alignment or registering areas.